Super high-frequency electromag



April 1953 w. w. SALISBURY 2,634,372

SUPER HIGH-FREQUENCY ELECTROMAGNETIC WAVE GENERATOR Filed Oct. 26, 1949FIG. I.

FIG. 2.

Sumter ,2

W/A/F/ELD I. SALISBURY Patented Apr. 7, 1 953 SUPER HIGH-FREQUENCYELECTROMAG- NETIC WAVE GENERATOR Winfield W. Salisbury, Cedar Rapids,Iowa, as-

signor to Collins Radio Company, Cedar Rapids, Iowa, a corporation ofIowa Application October 26, 1949, Serial No. 123.597

(Cl. ZED-36) 12 Claims. 1

This invention relates to electromagnetic wave generators, and moreparticularly to generators of the type employing interaction between anelectron beam and electromagnetic field lines through which the beampasses.

A principal object of the invention is to provide a novel genertaor forelectromagnetic waves of super high frequency, for example those of theorder of a millimeter or less in wavelength.

Another object is to provide a novel generator of monochromatic orhomogeneous radiation.

Another object is to provide a super high frequency electromagnetic wavegenerator employing an electron beam and a cooperating device forsetting up standing electromagnetic wave patterns transversely of thebeam.

A feature of the invention relates to the combination of a diffractiongrating and a wave refiector for setting up standing electromagneticwave patterns, and a source for producing and projecting an electronbeam through said pattern to generate any desired monochromaticradiation.

Another feature relates to an electron discharge device having means todevelop an electron beam of predetermined electron velocity, and adiffraction grating and wave reflector unit for setting up standingelectromagnetic waves transverse to the beam trajectory to generatemonochronmatic radiation.

Another feature relates to a monochromatic radiation generator employingmeans to develop an electron beam of predetermined electron velocity,and a unit excited by said beam and in the form of a diflraction gratingand wave reflector to set up standing waves transverse to the beamtrajectory, together with means for adjusting the trajectory angle ofthe beam with respect to the standing wave pattern to control thefrequency of the desired monochromatic radiation.

A still further feature relates to the novel organization, arrangementand relative location of parts which cooperate to provide an improvedmonochromatic generator of radiations of the order of one millimeter orless.

Other features and advantages not particularly enumerated, will beapparent after a consideration of the following detailed description andthe appended claims.

In the drawing,

Fig. 1 is a composite structural and schematic circuit diagram of aradiation generator according to the invention.

Fig. 2 is a simplified schematic showing of Fig. 1.

Figs. 3 and 4 are magnified views of part of Fig. 1 explanatory of theinvention.

There has been a great demand in certain fields of the radiation art,for an arrangement which can be used to generate homogeneous ormonochromatic waves of super high frequency, for example in the range ofone millimeter or less wavelength. The present invention provides suchan arrangement and is predicated upon the interaction which takes placebetween a beam of electrons of predetermined velocity and trajectory,with respect to a standing electromagnetic wave pattern set up in thespace through which the electron beam passes. In accordance with onefeature of the invention, the desired standing wave pattern is producedby a diffraction grating and a cooperating Wave reflector.

It is a well-known physical phenomenon that when a diffraction gratingis excited in any of the well-known ways, for example by electromagneticwaves, each aperture or inter-line spacing in the grating acts in thenature of a minute energy radiation source, for example ofelectromagnetic waves. If the wave front of the exciting waves isparallel to the plane of the grating openings, then each opening may beconsidered as a separate wave source, with all the radiations from theseveral openings in like phase. If, however, a wave reflector ispositioned at an angle with respect to the grating, there will be set upin the region between the grating and the reflector a standing wavepattern. Advantage is taken of this fact, by the present invention, toproduce the desired monochromatic or homogeneous radiation. Thus theangle between the reflector and grating determines the frequency whichwill be reflected. A different frequency is obtained for each angularsetting of the reflector.

Referring to Fig. 1, the numeral I represents any suitable enclosingbulb or envelope of glass or similar material which can be highlyevacuated. Mounted within the bulb adjacent one end thereof, is anelectron gun 2 of any construction well-known in the cathode-ray tubeart. This gun may comprise, for example, an electron emitting cathode 3,with its indirect heater element 4 for heating the cathode to thermionicemitting temperature; a first beam-focussing and accelerating anode 5; asecond beam-accelerating and focussing anode 6; and a cooperatingelectron collector electrode 1. Located between the gun 2 and collector1, is a set of beam deflector plates 8. 9. Located between the deflectorplates and the collector electrode '1, is a device It for setting up astanding wave pattern through which the electron beam passes on its wayto the collector.

In accordance with the invention, the device I comprises a diifractiongrating II of any construction well-known in the optical art, andconsisting of a multiplicity of spaced fine lines which are opaque towaves of the excitation frequency, and with the inter-line spacestransparent to such waves. For example, it may consist of a glass plateI2 on the planar surface of which there are provided the spacedelectrically-conductive lines I3. The number of these lines per unitlength of the plate I2, and the width of each line as well as thespacing between the lines should be chosen in accordance with thedesired range of the output radiation frequency that is desired from thedevice. For example, 10,000 lines per centimeter may be used to give aninterline spacing of .001 millimeter. The diffraction grating II ismounted so that the lines I3 extend transversely across the trajectoryof the electron beam, and the deflector plates 8 and 9 are arranged soas to control the beam trajectory in a plane perpendicular to the planeof the diffraction grating.

Mounted in spaced relation to the grating I I is a wave reflector I4which may consist of a hat metal plate having a highly polished surfacefacing the diffraction grating ll, that is to say it is in the form of amirror which has the property of reflecting the incident electromagneticwaves generated by the grating.

There is shown in Fig. 3, in magnified form, a portion of the gratingand the reflector I6, showing how the standing wave pattern is set upbetween the grating openings and the reflector. When the grating isexcited, the reflector it will be tuned by its angular position so as toreflect only one wavelength from the grating. This phenomena iswell-known to the optics field. For example, the position of lines in anabsorption spectrum may be obtained by allowing one of the lines toimpinge on a diffraction grating, and noting the angle where therefraction from the grating is obtained. This is a well-known procedurefor obtaining the wavelength of a particular visible radiation.Similarly in the present invention, the angle of the reflector picks upone wavelength from the diffraction grating and reinforces it, to obtaina standing wave pattern between the grating and the reflector. Theelectron beam which passes transversely through the standing wavepattern interacts with the electromagnetic wave produced by the grating,and increases its energy. Thus Fig. 3 shows the amplitude of thestanding waves in the absence of the electron beam, and Fig. 4 shows theamplitude of the standing waves in the presence of the electron beam.The frequency of the standing wave between the reflector and the gratingtherefore does not change for a particular setting of the reflector. Theelectron beam passing therethrough, merely increases the amplitude ofthe standing wave pattern, or saying the same thing, it merely increasesthe energy contained in the standing wave. As the standing wave and thebeam interact, the direct current beam of electrons which are passingthrough, tend to group or bunch, as they say in the magnetron field, andthis invention is of the nature of a very high frequency parallel planemagnetron. The energy is taken off by the pickoif II, or by an energyreceiver in the space between member II and member I, and the energyinincreases directly as the velocity of the electron beam increases. Inother words, by adjusting the positive potential of the electrode I, orin any other way adjusting the velocity of the electrons in the beam IS,the amount of energy that can be picked up by the device I'I canlikewise be controlled.

Thus for the dimensions of the grating lines and spaces as given above,the electrodes of the electron gun and the electrode I can be energizedto produce a beam having electrons with an electron velocity of 50kilovolts, and with the reflector I4 inclined at an angle of 20 degreeswith respect to the plane of the grating to generate radiationfrequencies of the order of 5,000 Angstrom units wavelength. It will beunderstood, of course, that in order to control the frequency of thegenerated monochromatic or homogeneous radiation, the angle between thereflector I4 and the diffraction grating can be adjustable. For example,the reflector I4 may be pivotally supported by a suitable member IB froma wall of the envelope I, and one end of the plate I4 may be urgedupwardly by an appropriate spring I9, while the opposite end of theplate can be biased by means of a suitable electromagnet 20- external ofthe envelope. For this latter purpose, the plate I4 may be of magneticmaterial, or it may carry at its right-hand end a magnetic member whichcooperates with the electromagnet 20.

The magnet 20, therefore, may be used as a means for modulating thefrequency of the generated monochromatic radiation merely by applyingcorresponding varying excitations to the winding of the magnet 20.

The grating II does not require any external excitation source in orderto initiate the action of the tube. Since the grating H is always atsome temperature above absolute zero, there is enough energy radiatedfrom it to initiate the operation of the tube as an oscillationgenerator when the cathode 3 is in operation and when the appropriatepotentials are applied to the several electrodes as above described.However, it will be understood that if desired, the grating II may beexcited by an external source of electromagnetic waves of any knowntype, the wavelength of which is correlated with the inter-lined spacingof the grating lines as is well-known in the diffraction grating art.

While certain embodiments have been described herein, it will beunderstood that various changes and modifications can be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. Super high frequency radiation generating apparatus, comprising meansto develop a beam of electrons, means including a diifraction grating toset up a standing electromagnetic wave pattern through which the beampasses to produce a high frequency radiation controlled by theinteraction between the beam and said pattern.

2. Super high frequency generating apparatus. comprising means todevelop a beam of electrons, means including a diffraction grating and acooperating Wave reflector to set up a standing electromagnetic wavepattern through which the beam passes to produce a predeterminedradiation frequency.

3. Super high frequency radiation apparatus, comprising means to developa beam of electrons, a diffraction grating and a cooperating wavereflector for setting up a standing electromagnetic wave pattern throughwhich the beam passes, and means to adjust the angular relation betweensaid grating and reflector to control the frequency of the generatedradiation.

4. Super high frequency apparatus, comprising an evacuated enclosingenvelope, an electron gun for developing a beam of electrons, anelectron collector, and a device located between said gun and electrodefor setting up a standing wave pattern through which the beam passes,said device including a diffraction grating.

5. Super high frequency apparatus, comprising an evacuated enclosingenvelope, an electron gun for developing a beam of electrons, anelectron collector electrode, and a device located between said gun andelectrode for setting up a standing wave pattern through which the beampasses, said device including a diffraction grating, and a cooperatingwave reflector.

6. The method of generating homogeneous electromagnetic wave radiation,which comprises developing an electron beam, setting up a standingelectromagnetic wave pattern under control of a series of separate wavesources and a common wave reflector displaced along the beam tra-Jectory, and controlling the angular relation between said sources andreflector to determine the radiation frequency, said pattern being setup by interaction between a diffraction grating and a wave reflector.

'7. The method of generating homogeneous electromagnetic wave radiation,which comprises developing an electron beam. setting up a standingelectromagnetic wave pattern under control of a series of separate wavesources and a common wave reflector displaced along the beam trajectory,and controlling the angular relation be tween said sources and reflectorto determine the radiation frequency, the frequency of the radiationbeing controlled by adjusting the angular relation between a diffractiongrating and a cooperating reflector between which the electron beampasses.

8. The method of generating homogeneous radiation, comprising developinga beam of electrons, exciting a diflraction grating by theelectromagnetic waves from said beam to set up a standing wave patternalong said grating, passing said beam through said pattern, andadjusting said pattern in accordance with the desired radiationfrequency.

9. The method according to claim 8, in which the standing Wave patternis set up between said diffraction grating and a cooperating waverefl-ector.

10. A super high frequency tube, comprising an evacuated envelope, saidenvelope containing an electron gun, an electron collector electrode, adiffraction grating extending parallel to the electron beam between thegun and collector, a reflector member cooperating with said diffractiongrating to set up therebetween a predetermined standing wave pattern,and means within the envelope to conduct the generated radiation to apoint external of the envelope.

11. A tube according to claim 10, in which means are provided to controlthe frequency of the standing waves.

12. A tube according to claim 10, in which said reflector is mounted inangular spaced relation with respect to said grating, and means areprovided for adjusting the said angular relation and thereby todetermine the frequency of the generated radiation.

WINFIELD W. SALISBURY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,064,469 Haeff Dec. 15, 19362,154,127 Hollmann Apr. 11, 1939 2,170,251 Schlesinger Aug. 22, 19392,361,998 Fleming-Williams Nov. 7, 1944 2,368,031 Llewellyn Jan. 23,1945 2,409,991 Strobel Oct. 22, 1946 2,409,992 Strobel Oct. 22, 19462,449,975 Bishop et al Sept. 28, 1948 2,466,065 Weichardt Apr. 5, 19492,493,706 Washbume et al. Jan. 3, 1950

